Some of the abbreviations used in this application are as follows:                CCCH Common Control Channel        DCCH Dedicated Control Channel        DRNC Drift Radio Network Controller        DTCH Dedicated Traffic Channel        FACH Forward Link Access Channel        IMSI International Mobile Subscriber Identity        PCCH Paging Control Channel        PCH Paging Channel        PLMN Public Land Mobile Network        P-TMSI Packet Temporary Mobile Subscriber Identity        PSCH Random Access Channel        RNC Radio Network Controller        RNTI Radio Network Temporary Identity        RRC Radio Resource Control        TMSI Temporary Mobile Subscriber Identity        UE User Equipment        UMTS Universal Mobile Telecommunication System        UTRAN UMTS Terrestrial Radio Access Network        
For clarification of common terms used in this document, an overview of certain cellular telecommunication system configurations is presented in the following.
Proposals for third-generation systems include UMTS (Universal Mobile Telecommunications System) and FPLMTS/IMT-2000 (Future Public Land Mobile Telecommunications System/International Mobile Telecommunications at 2000 MHz). In these plans cells are categorised according to their size and characteristics into pico-, nano-, micro- and macrocells, and an example of the service level is the bit rate. The bit rate is the highest in picocells and the lowest in macrocells. The cells may overlap partially or completely and there may be different terminals so that not all terminals necessarily are able to utilise all the service levels offered by the cells.
FIG. 1 shows an exemplary block diagram of a possible structure of a third generation cellular network. Such networks typically comprise a core network 50 connected to one or more radio access networks 40 (RAN). Such radio access networks are often referred to as UTRAN networks (UMTS Terrestrial Radio Access Network). The radio access networks typically comprise at least a plurality of base stations 20a,20b, 20c (BS) for realizing the radio connections to mobile stations 10a,10b, and at least one radio network controller 30 (RNC) for controlling the base stations. The radio network controllers are connected to a mobile switching center (MSC) 60 in the core network.
A third generation UE can be in many different states in relation to the network. If no connections are present, the UE is in the idle mode. When at least one signalling connection exists, the UE is in connected mode. The connected mode has two main states: a URA connected state and a cell connected state. In the URA connected state, the position of the UE is known on URA (UMTS Registration Area) level. A URA consists of a plurality of cells within a certain geographical area. In the cell connected state, the position of the UE is known in the cell level. All data transmission is effected in the cell connected state.
From the viewpoint of radio resource allocation, a UE in connected mode i.e. when RRC connections exist has two main states: dedicated channel state (DCH) and common channel state (CCH).
In dedicated channel state the UE uses dedicated radio interface resources for the connection with UTRAN. There is one dedicated radio link for each cell included in the Active Set, i.e. the set of cells used by the UE. The Active Set may contain one or more cells.
In common channel state the UE shares a common channel with other users. The common channel state the UE may be in RACH/FACH or RACH/PCH substates. In RACH/FACH state the position of the UE is known at cell level, i.e. the UE is always connected to one cell. In RACH/PCH state the position of the UE is known either at cell level or at URA level. DCH to CCH state transition may occur for example as a result of the following RRC procedures:                Transport channel reconfiguration, in which a transport channel is changed from a dedicated to a common channel, for example for a NRT bearer.        Radio access bearer (RAB) release, in which at least one bearer is released, and the last remaining one is a non-real time (NRT) bearer which is currently not active or is which is configured to use common channels.        Physical channel reconfiguration, which procedure may assign, replace or release a set of physical channels used by an UE. A physical channel reconfiguration procedure may also change the used transport channel type and RRC state.        Radio access bearer (RAB) reconfiguration, in which parameters for a radio access bearer or a signalling link are reconfigured to reflect a change in required QoS level. A RAB reconfiguration procedure may comprise for example changing of RLC parameter, changing of multiplexing priority for DTCH/DCCH, changing of DCH scheduling priority, changing of TFS for DCH, change of TFCS, assigning or releasing of physical channel(s) and changing of used transport channel types.        
The signalling in the case of the four previous procedures is similar: they are started by the serving RNC which sends a XXX message to the UE, which replies with a XXX Complete message, in which XXX refers to the particular procedure in question.
In the transition from DCH to CCH—cell connected state, the cell that will be initially used in the CCH state needs to be selected and indicated. A known way of selecting and indicating the initial cell is the use of a cell update procedure started by the UE. In this method the UE selects the cell, and sends a cell update message using the RACH channel of the selected cell. The network replies by sending a cell update confirm message via the corresponding FACH channel. This solution causes too much signalling on the RACH/FACH channels. Further, the UE may not know all details which affect the optimality of the cell selection. For example, the network may for various reasons prefer that the UE selects a macro cell, or a cell that is controlled by the SRNC.
Another known solution is that the XXX complete message is sent by the UE on the RACH channel of the selected cell after the DCH is released. In this case the XXX Complete message should be acknowledged by the network to ensure that the message has gone through, which results in a similar signalling load as the cell update method.